The Atlanta Falcons, New York Giants, San Francisco 49ers and Chicago Bears went into Sunday's Week 10 NFL action looking to build on their status as powerful NFC division leaders. That didn't happen.

The Falcons are no longer undefeated. The Giants remain in a familiar November slump. The Niners settled for a tie when they were highly favored at home. The Bears capped it off by producing no offense at home against the AFC’s best team.

Given the grind-it-out nature of a long season that's only barely past the halfway point, those hiccups will happen, especially in a league where no team is without flaws and where no opponent can be taken lightly. Here's a look at the key issues the four first-place teams must sort out soon:

Falcons: Running the ball, stopping the run. There wasn't much difference between Atlanta and New Orleans during their shootout in the Superdome, which the Saints turned into a 31-27 win over their NFC South archrivals. One statistic, however, was glaring. The Saints outrushed the Falcons, 148-46. This is problematic on two counts.

First, the Falcons should have had rushing success with power back Michael Turner, given the Saints have been gashed for big chunks between the tackles all season. Second, the Falcons' defense got pounded on by tough running from Chris Ivory and Mark Ingram, especially on Ivory's 56-yard scoring burst.

Turner produced just 15 yards on his 13 carries. There's no doubt Matt Ryan, who threw for a career-high 411 yards in the loss, is having a great season in a high-flying, up-tempo passing attack. But the Falcons need to stick with the run to both take pressure off Ryan and help keep their defense from wearing down.

Giants: Offensive consistency and discipline. Eli Manning is battling through the toughest stretch we've seen in quite some time, which continued in an embarrassing 31-13 loss at Cincinnati. Now that the Giants have gotten their rushing attack going again, it should reduce the potential for other offensive mistakes, but it's been just the opposite.

Uncharacteristic pass-protection issues have contributed to Manning's giveaway woes. He threw two more interceptions and lost a fumble, and the Bengals sacked him four times. Running back Ahmad Bradshaw also lost a fumble, and wide receiver Victor Cruz dropped a potential touchdown pass. Tom Coughlin isn't happy about the play of Manning and the entire group, and as usual, he has something to get on his team about. As we've seen twice before, Coughlin is capable of cleaning up the act in time for a Super Bowl run.

49ers: Run defense, big-play defense. The Niners lost starting quarterback Alex Smith to a concussion, but having to use young backup Colin Kaepernick wasn't the problem in the 24-24 tie with the Rams. Kaepernick ran the offense well and maintained its ball-control prowess.

The Niners' defense, meanwhile, couldn't get off the field. They were thrown off balance by St. Louis' balanced attack, similar to what they saw in losses to the Vikings and Giants. They got worn down by Steven Jackson spearheading a 159-yard rushing effort. Quarterback Sam Bradford, save for two sacks from Aldon Smith, dealt with little pressure and could spread the ball around well.

Because the Rams were able to keep on schedule and convert some key third downs in the second half, the Niners couldn't do what they do best after they usually stuff the run—get after the passer with their 3-4 pressure and force takeaways. They were so good at consistently capitalizing on mistakes a year ago. Now that effect is only coming against bad offenses. That needs to change when the stakes and offensive competition are raised in the playoffs.

Bears: Offense in general. Chicago dealt with some added adversity in its 13-6 loss to Houston. If it was not enough to face a swarming Texans defense, the windy, rainy conditions and losing quarterback Jay Cutler to a first-half concussion raised the degree of difficulty. But on a night when the Bears' pass protection played over its head and wide receiver Brandon Marshall made some tough catches, everything else let them down. The run blocking wasn’t there for Matt Forte, and the complementary receivers could not come through. The Bears keep putting themselves in uncomfortable, unmanageable third-down situations because of penalties and an inability to win on first and second down.

The Bears have relied on their defense to provide much of their offense all season, but their two interceptions against the Texans didn’t become scoring returns. Even if Cutler is able to bounce back and play, this team has plenty to fix in terms of execution and playbook to operate more consistently.

Considering Atlanta, New York, San Francisco and Chicago all showed chinks in their armor, another NFC contender should have been pleased: the idle Green Bay Packers.

Patriots' defensive woes reappear

On a day when fellow AFC division leaders Denver and Baltimore had statement victories against overmatched opponents, New England needed a late Devin McCourty interception to preserve a 37-31 escape from Buffalo.

What should be most disconcerting to Patriots coach Bill Belichick is that his defense, after a bye, looked lost while giving up 481 total yards to the Bills, who pretty much did what they wanted running and passing. If it weren't for red zone turnovers by Ryan Fitzpatrick and Fred Jackson, the Patriots would have been staring at another shocking home loss.

There's no immediate concern that the Patriots won't win the division, as the Jets and Dolphins suffered losses Sunday. But there will be a big concern if the Pats need to face Peyton Manning or Joe Flacco again in the playoffs, as both quarterbacks are supported by strong running games. The Patriots still need to face Matt Schaub and the Texans before then (Week 14).

Considering the way the Broncos and Texans are playing on defense, and that the Ravens are still hanging in well on that side of the ball despite mounting injuries, the Patriots—even armed with Tom Brady—fall to fourth in the pecking order for ultimate AFC supremacy. And soon, they might be fifth behind the Steelers.

Injury update

Michael Vick, QB, Eagles (eye, concussion). Vick had been taking such a beating behind Philadelphia's offensive line that it was no surprise that he took a knockout hit against the defensively strong Cowboys. With the Eagles (3-6) out of contention now, they may have an opening to give rookie Nick Foles a longer look as the quarterback of the future.

Alex Smith, QB, 49ers (concussion). Second-year backup Colin Kaepernick provided more than an athletic spark in relief of Smith with his combination of confident passing and well-timed running against the Rams. The offense came back strong to create a 24-24 tie with Kaepernick playing well in the fourth quarter. But there's no question that the Niners would stick with a healthy Smith.

Jay Cutler, QB, Bears (concussion). Cutler wasn’t immune to the rash of head injuries, as he was roughed up by Houston's defense in the first half of Chicago’s Sunday night loss. The offense wasn’t doing much with Cutler but completely stagnated with backup Jason Campbell at the helm. Now the Bears have to hope Cutler will be ready for a Monday night showdown with the 49ers.

Elvis Dumervil, DE, Broncos (shoulder). Denver's defense has been outstanding of late, led by its best player, outside linebacker Von Miller. But Dumervil is its second-best performer and a great edge rusher. If Dumervil must miss significant time, it would be a significant blow to a red-hot group.

Cliff Avril, DE, Lions (concussion). Avril was banged up in the tough loss at Minnesota, and Detroit struggled to put pressure on Christian Ponder without him. With the back end of the Lions' pass defense falling apart, losing their best edge pass rusher for an extended time would add to their challenges.

Quincy Black, LB, Buccaneers (head, neck). With Black on the strong side helping Mason Foster and rookie Lavonte David at linebacker, the Bucs have fielded the NFL's best run defense in the first season under Greg Schiano. Black is expected to be OK after the scare of being carted off on a stretcher against San Diego, but Tampa Bay is a little thin on adequate every-down replacements.